How high above sub-floor should pipe for toilet flange be left when tiling?
We're going to install a tile floor over Ditra in our remodel in progress bathroom. We have 4" abs pipe going up to the toilet and plan to install a flange that slides inside the 4" abs flange that installs inside the pipe. It's an Oatley with a stainless steel ring and knock out center. The plumber who installed the piping cut the pipe off flush with the plywood sub-floor.
My concern is that the flange fitting with a typical tapered interference fit will not "glue up" properly when installed on top of tile another 1/2" of so above the sub-floor. When I dry test fit the flange 1/2" from seated it seems very loose and only comes tightish when seated.
It's not too late to go down below, cut off the 4" abs, insert a coupler and add a longer piece above. Does that sound like a good ideal or might one of the expansion based flanges be a better idea. Install tile slide in flange. Tighten up expansion screws. set toilet and be done?